Invited Commentary

Abstract

Undersizing mitral annuloplasty (UMA) has emerged as a mitral repair technique of choice to correct ischemic mitral regurgitation (IMR). Despite the unphysiological leaflet coaptation that results from this repair and the potential deleterious impact that restricting mitral annular dynamics and basal myocardial contraction may have on left ventricular function, extensive surgical experience with UMA and its procedural ease makes this a procedure of choice. However, to achieve better long-term patient outcomes after UMA, the adverse impact of UMA on the valve and the ventricle needs to be better understood. In this study, Pantoja and colleagues [1Pantoja J.L. Morgan A.E. Grossi E.A. et al.Undersized mitral annuloplasty increases strain in the proximal lateral left ventricular wall.Ann Thorac Surg. 2017; 103: 820-827Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar] use a finite element model of an IMR-like left ventricle to demonstrate that UMA impacts basal myocardial mechanics and acutely alters left ventricular shape. Specifically, the end-diastolic longitudinal strain in the lateral left ventricular wall was elevated when compared with the preoperative configuration, but the fiber strain in the same region was decreased. The authors conclude that UMA induced changes in left ventricular shape and that mechanics can trigger continued remodeling of the ventricle and result in recurrent IMR and poor ventricular function. This is a nicely done computational study, albeit with some limitations, which follow:1.Preannuloplasty annular size and shape—in the clinical scenario, the mitral annular sizes, shapes, and extent of dilatation differs significantly between patients, and the effect of an annuloplasty ring on each annulus may be variable. Despite using 5 sheep-specific models in this study, the variability in annular geometry and its impact on postannuloplasty strains were not investigated.2.Impact of IMR correction—Annuloplasty acutely abolishes IMR and thus reduces. Reduced end-diastolic strain may reduce the impact that the ring may have on the ventricular shape and mechanics. The computational model does not consider the physiological effects of the ring on the ventricle.3.The distinction of the myocardium into layers is only hypothetical and not ultrastructure driven in this model. Specifically, the infarcted myocardium is thinned, lacks distinct layers, and is often stiffened from fibrosis. The computational model did not seem to consider these regional structural features, which may have an impact on the reported strains. Notwithstanding these limitations, this study provides some preliminary insights into the deleterious impact that undersizing annuloplasty may have on the left ventricle. However, whether it causes continued left ventricular remodeling or impairs systolic function remains speculative at best and needs careful experimental validation. In 2012, Shudo and coworkers [2Shudo Y. Nakatani S. Sakaguchi T. et al.Left ventricular mechanics following restrictive mitral annuloplasty for functional mitral regurgitation: two dimensional speckle tracking echocardiographic study.Echocardiography. 2012; 29: 445-450Crossref PubMed Scopus (4) Google Scholar] investigated left ventricular mechanics at 4 weeks after UMA in patients with IMR and reported that ejection fraction and longitudinal strains were largely unaltered. Radial and longitudinal strains were improved at the mid and apical levels but were unaltered at the base of the ventricle. Left ventricular twist was significantly elevated in these patients after UMA, compared with their preoperative measurements. The discrepancy between such improved left ventricular mechanics in patients who underwent UMA and the adverse impact suggested in this simplified computational model will need to be explained for clinical translation of these findings. Undersized Mitral Annuloplasty Increases Strain in the Proximal Lateral Left Ventricular WallThe Annals of Thoracic SurgeryVol. 103Issue 3PreviewRecurrence of mitral regurgitation (MR) after undersized mitral annuloplasty (MA) for ischemic MR is as high as 60%, with the recurrence rate likely due to continued dilation of the left ventricle (LV). To better understand the causes of recurrent MR, we studied the effect of undersized MA on strain in the LV wall. We hypothesize that the acute change in ventricular shape induced by MA will cause increased strain in regions nearest the mitral valve. Full-Text PDF